1. Field of the Invention
The present invention relates to a system for the contact-free or contactless identification of articles, notably metal articles such as, for example, gas cylinders or bottles.
2. Description of the Prior Art
A known way of locating and identifying such articles is to affix electronic labels to them. Such a label is provided with a device for the reception and transmission of electromagnetic waves coupled with an electronic module enabling the processing of the received signals and the re-transmission of other signals, comprising notably a message for the identification of the label, and hence of the article to which it is affixed. Furthermore, the system has an electromagnetic wave tranmission/reception or transceiver device to transmit information elements between a data terminal and said electronic label.
The reader fulfils several functions and is notably used to:
send the label the energy needed for its functioning, the label lacking any specific, independent energy source, PA1 send the label data elements coming from the terminal, it being possible for these data elements to be recorded, if necessary, in a memory with which the label is provided, PA1 receive data elements that come from the label and are specific to it, notably with a view to its identification.
To carry out these various transmissions, the transceiver device of the reader has an antenna constituted, for example, by a coil with a ferrite core used for transmission and reception.
The label also has an antenna to receive the electromagnetic waves transmitted by the reader, the same antenna being used also to transmit data elements to the reader. In reception, the antenna constitutes a means for the reception, by induction, of the energy coming from the reader as well as a means for the reception of the data elements sent out by this reader. The antenna is connected to an electronic circuit, for example an electronic "chip", comprising means necessary for the demodulation of the signals received by the antenna, their decoding and memorizing, as well the encoding and modulation of the signals to be re-transmitted.
A major problem of these systems is that of enabling the label to receive the energy needed for its operation with maximum efficiency so as to make it possible to reduce the power of the electromagnetic radiation sent out by the reader and limit the amount of space required by the antennas, and enable a transmission of energy and signals without being subjected to an excessively short distance of transmission.
To attempt a resolution of this problem, it has already been proposed to make a ferrite cylinder type of label antenna formed by a cylindrical ferrite piece comprising, on one of its plane faces, an annular groove in which a coil is housed. Such an antenna is necessarily fixed to the article to be identified with its axis perpendicular to the surface of the article and, owing to the relatively great height of the ferrite cylinder, has a cumbersome space requirement in the axial direction. A known way of overcoming this problem is to embed the label in the surface of the article. For example, there is a known way of placing labels of this type in a housing hollowed out in the button of the gas cylinder valve. Consequently, the antenna is necessarily small-sized.
The antenna of the reader is made similarly by means of a coil whose axis has to be placed substantially in the direction of the axis of the antenna of the label to provide for the best possible transmission of energy. For reasons of space availability, it is practically impossible to increase efficiency by means of the approach that consists in increasing the diametric size of the label in order to pick up more of the flux lines emitted by the reader. It has thus turned out to be the case that the distance between the reader and the label can hardly exceed 5 mm with such a system.
Another approach envisaged is that of making the antenna of the label in the form of a coil surrounding an elongated ferrite rod, for example 15 mm long and 3 mm wide.
In order that the flux lines of the magnetic field may pass into the ferrite rod in the axial direction of the coil, this coil should be substantially parallel to the surface of the article to which the label is affixed. A first drawback of this arrangement is that, in order to enable the transmission of energy and data between a reader of the above type and the label, the antenna of the reader should be oriented so as to have its axis oriented substantially in the axial direction of the coil of the antenna of the label. The result thereof is that it is impossible to read the label reliably without seeing to the relative orientation of this label with respect to the reader. Furthermore, it is necessary to place the label in a place where it is mechanically protected. In the case of gas cylinders, this is achieved by placing the label close to the valve, inside the protective bell or socket of the valve, in a plane substantially perpendicular to the axis of the cylinder. To ensure efficient transmission of energy between the reader and the antenna of the reader, the antenna of the reader would have to be placed in an axial alignment with the antenna of the label. This is practically impossible inside the bell for reasons of space requirements, and if the reader is placed outside the bell, the latter forms a shield that greatly disturbs the transmission.
Consequently, although labels with antennas of the ferrite rod type have certain advantages, notably as regards the amount of space required, they cannot be read by a reader reliably and easily when they are placed on many types of articles, notably gas cylinders.